Production of aluminum trialkoxide and aliphatic alcohols



United States Patent Office 3,450,735 Patented June 17, 1969 3,450,735 PRODUCTION OF ALUMINUM TRIALKOXIDE AND ALIPHATIC ALCOHOLS Allan J. Lundeen and James E. Yates, Ponca City, Okla, assignors to Continental Oil Company, Ponca City, Okla., a corporation of Delaware No Drawing. Filed Nov. 14, 1966, Ser. No. 593,698 Int. 'Cl. C07f 5 06' US. Cl. 260-448 7 Claims ABSTRACT OF THE DISCLOSURE During the oxidation of trialkylaluminum compounds with oxygen, isopropanol is added to suppress the formation of side products. Acetone subsequently formed is removed by heating.

This invention relates to an improved method for the production of aluminum trialkoxide compounds and primary aliphatic alcohols. More particularly, it relates to the production of primary aliphatic alcohols by the oxidation of trialkylaluminum compounds and subsequent hydrolysis of the resultant aluminum al'koxide compounds.

Various methods have been proposed for producing primary aliphatic alcohols. A comparatively recent process for synthesizing these alcohols has been based on the oxidation of tri-alkylaluminum compounds to form aluminum alkoxides which are then hydrolyzed to form alcohols. This process has not heretofore been entirely satistactory because of the formation of by-products and the resultant lower yield of the desired alcohols. US. Patent 3,257,468 discloses that the yield of a primary alcohol obtained by the aforedescribed process can be improved by carrying out the later stages of the oxidation in the presence of an aluminum alcoholate derived from a secondary alcohol, particularly, aluminum isopropoxide. The aluminum alcoholate is added when the oxidation is no more than two-thirds complete. This method has resulted in improved yields of alcohol, but its application is restricted in that the aluminum alcoholate must be added when the oxidation reaction is no more than twothirds complete. Use of the aluminum alcoholate compound also increases the cost of the process.

An object of this invention is to provide an improved process for the production of aluminum alkoxides.

Another object of this invention is to provide an improved process for the production of primary aliphatic alcohols.

Another object is to provide a more economical process for the manufacture of primary aliphatic alcohols.

Further objects and advantages will become apparent from the following description.

Briefly, we have discovered an improved process for preparing aluminum trialkoxide compounds and primary aliphatic alcohols which comprises conducting the latter stages of the oxidation of trialkylaluminum compounds with molecular oxygen to aluminum alkoxide compounds in the presence of a quantity of added isopropanol. We prefer to add the isopropanol when oxidation of aluminum trialkyls to the trialkoxide compounds is between about 80 to about 90 percent complete. However, the addition of isopropanol can be made when oxidation is only 70 percent complete or can be delayed until oxidation is about 100 percent complete. Acetone, generated during the reaction after addition of isopropanol, subsequently is removed and, as in the prior art, the alcohol is obtained by hydrolyzing the aluminum alkoxides. The acetone removed can be hydrogenated to isopropanol and recycled.

The trialkylaluminum compounds included within the scope of this invention are those wherein the aluminum is bonded to a primary carbon atom, that is, a carbon atom having attached thereto two hydrogen atoms, and include such compounds wherein the carbon content of the alkyl radicals varies from 2 to canbon atoms or even more. Although theoretically there is no limit to the number of carbons in the alkyl radical that can be used, we generally prefer to employ a trialkylaluminum compound wherein the carbon content of alkyl radicals varies from 2 to 22. Obviously the alkyl radicals of the trialkylaluminum compound may be the same or difierent. If a compound is used wherein the alkyl radicals are the same, one alcohol is produced. If, on the other hand, a compound is used wherein the alkyl radicals are diiferent, a mixture of alcohols is formed.

For example, triethylaluminum can be oxidized to aluminum ethoxide in the presence of isopropanol and ethanol obtained by hydrolysis of the aluminum ethoxide. Similarly, tripropylaluminum, tributylaluminum, tripentylaluminum, and trihexylaluminum can be oxidized in the presence of isopropanol to the corresponding aluminum propoxide, aluminum butoxide, aluminum pentoxide, and aluminum hexoxide, and by hydrolysis the corresponding alcohols, propanol, butanol, pentanol, and hexanol, can "be obtained. Other trialkylaluminum compounds which can be employed are triisobutylaluminum,

, trioctylaluminum, tri-(2-ethylhexyl)-aluminum, tridodecylaluminum, trioctadecylaluminum, ethylbutylhexylaluminum, and the like.

Particularly useful for oxidation and subsequent conversion to the primary aliphatic alcohols is the mixture of trialkylaluminum compounds known as growth product which is obtained by the well known growth reaction in which a low molecular weight mono-olefin, such as ethylene, propylene, butene, etc., is combined with a low molecular weight aluminum trialkyl, such as, for example, an aluminum trialkyl having the alkyl substituents containing from about 2 to 24 carbon atoms. The resultant growth product comprises a trialkyl compound in which the alkyl groups vary widely in molecular weight. The preparation of growth product is discussed in a number of US. patent, including US. Patent 3,249,648. The composition of a typical growth product is presented in Table I.

TABLE I Composition of a growth product Alkyl group of trialkyl- Mole percent aluminum compound:

in growth product Mean number of moles of ethylene added per mole of trialkylaluminum=4.00.

As to the oxidizing agent, it may be air, enriched air, pure oxygen, etc.

As discussed in US. Patent 3,257,468, the oxidation of the trialkylaluminum compounds to the aluminum alkoxides is not quantitative; but certain by-products are also obtained, some in a relatively high yield. These by-products include carbonyl compounds (for example, aldehydes), esters, and hydrocarbons but are not limited to those only, as other by-products also may be produced. While we do not wish to be bound by any theory as to how these by-products are formed, we believe that the following is a correct explanation.

The oxidation of aluminum alkyls is believed to be a two-step process involving reactions of the type indicated by Equations 1 and 2.

f R--CII radical is the equivalent of the R radical of reaction (1),

R being an alkyl radical. The R alkyl radicals of reaction (1) are not to be considered as all necessarily identical.

If the aldehyde of reaction (5) is not removed, it will undergo a further reaction to yield an ester (Tischtschenko reaction) and unsaturated carbonyl containing-compounds (aldol condensation) giving, ultimately, a complex mixture comprising an alcohol, ester, aldehyde, hydrocarbon, unsaturates, etc.

We have found that the presence of isopropanol during the later stages of the oxidation reduces the amount of aldehydes, ketones, other carbonyl-containing products, and other by-products in the final product with a corresponding increase in the yield and quality of the desired alcohol. We do not know why improved results are obtained by the use of isopropanol; it may be that the isopropanol chemically reduces some intermediate in the aldehyde forming process or the aldehyde itself. The important fact is that the presence of the isopropanol effects the increased yield of alcohol. This is particularly surprising since normally isopropanol and the partially oxidized aluminum trialkyl would be expected to react directly and to form saturated hydrocarbons.

The method of our invention can be applied either to a batch process for the manufacture of aluminum trialkoxide and normal aliphatic alcohols or to a continuous process. We will first describe it as applied to a batch process in which the trialkylaluminum compound to be oxidized and hydrolyzed to alcohols is growth product obtained from the reaction of aluminum triethyl and ethylene.

A-quantity of growth product in an inert paraffinic hydrocarbon diluent is placed in a reactor vessel. Air, oxygen, or other oxygen containing gas is bubbled through the mixture of growth product and inert diluent. The temperature of the exothermic reaction is controlled by continually circulating a portion of the reacting mixture through a cooling loop or coil. The effluent gas from the reaction can :be monitored for oxygen content and the appearance of carbonyl compounds in the reaction mixture monitored by testing samples in infrared adsorption equipment.

When oxidation of the growth product is determined through analysis of the efiiuent gas to be between and 100 percent complete (or preferably between and percent complete), or when the appearance of carbonyl compounds is indicated by infrared adsorption measurements, isopropanol is added to the reactor. The quantity added is equal to between about 0.5 and about 20 percent by weight (or preferably between about 5 and about 10 percent by weight) of the weight of growth product originally added to the reactor. Oxidation is then completed.

When oxidation of the growth product to the equivalent trialkoxide product is completed, the mixture of aluminum trialkoxides, inert diluent and any other compounds is either retained in the reactor or transferred to another vessel where, in either instance, it is heated at a rate and to a temperature that will permit controlled evolution of acetone and excess isopropanol from the mixture. If acetone is allowed to remain too long in the mixture, unwanted side products can form from it. It is, however, equally important to allow sufiicient time for the isopropanol to react with aldehydes and aldehyde precursors present in the reaction mixture. Although heating is a preferred method of vaporizing and removing acetone and isopropanol, other methods of removal are possible such as bubbling an unreactive gas through the reaction mixture, adsorption, or stripping.

When the acetone and excess isopropanol have been removed from the mixture of aluminum alkoxides, diluent, and side products, the mixture is treated to recover the aluminum alkoxides, for example by spray stripping. The recovered aluminum alkoxides then are hydrolyzed and the resulting hydrolized product is fractionated into fractions containing normal aliphatic alcohols of graduated molecular weights.

Pilot plant tests have demonstrated the working of our invention. In these tests growth product of a composition similar to that in Table I was oxidized and converted to alcohols. In each of the tests, about 80 gallons of growth product mixed with an inert hydrocarbon diluent was placed in a reactor and oxidized by bubbling air through the mixture. Pressure in the reactor during oxidation was about 40 p.s.i.g.; the temperature during the first 30 to 40 percent of oxidation was about 96 F. and during the remainder of the oxidation was about 90 F. Isopropanol was added when continual infrared analysis indicated the appearance of carbonyl compounds. This point varied between 83 and 92 percent completion of the oxidation reaction. After oxidation was completed, the oxidation mixture was first heated under a pressure of 100 mm. of mercury to a temperature of to F. When most of the acetone was removed, the pressure was raised to mm. of mercury and the temperature increased to F. Finally, the pressure was reduced to 50-100 mm. of mercury and the temperature raised to- 250-300" F. to remove the last of the isopropanol.

After this step, the mixture of oxidized growth product and solvent was stripped in a two-stage stripper. The overhead product from the stripper constituted diluent and any by-products formed. The bottom product recovered and removed from the stripper constituted relatively pure aluminum trialkoxide which was then hydrolyzed with sulfuric acid, neutralized with caustic, and water-washed The crude alcohol product thus obtained was then fractionated into several cuts comprising a butanol-water cut, alcohols containing 6, 8, and carbon atoms, alcohols containing 12 and 14 carbon atoms, alcohols containing 16 and 18 carbon atoms, and the residual bottoms containing alcohols of 20 or more carbon atoms and other high boiling point residue. Each of the alcohol cuts was then hydrogenated, a standard finishing step which improves the quality of the alcohol.

Two control tests, A and B, were made in which no isopropanol was added to the growth product during oxidation. T-wo tests, C and D, were made in which 1 pound of isopropanol was added during oxidation for each 10 pounds of growth product placed in the reactor. One run, E, was made in which 0.5 pound of isopropanol was added during oxidation for each 10 pounds of growth product placed in the reactor. \In tests C and D the percent increase in the yield of normal alcohols of 6 to 18 carbon atoms per molecule averaged 5.4 percent; correspondingly, intest E a 2.8 percent yield increase of C to C alcohols resulted. The addition of 1 pound of isopropanol per 10 pounds growth product caused an average decrease of 22 weight percent in the loss of material to the residual bottoms containing alcohols of 20 or more carbon atoms per molecule. This was significant in that this decrease of weight of residual bottoms (a less desirable and valuable fraction) represents an increase in the yield of the more valuable lower molecular weight alcohols. A 5 weight percent reduction in the amount of material lost to the overhead product in the stripping process also resulted.

In addition to increasing the yield of alcohols having 6 to 18 carbon atoms per molecule, the' quality of the alcohol product was improved. The alcohol fractions ob tained from the run using 1 pound of isopropanol per 10 pounds of growth product were analyzed and compared with the corresponding alcohol fractions obtained without the isopropanol treatment. The proportion of undesirable carbonyl compound, esters, and unsaturated compounds was reduced considerably as shown in Table II.

Table II correlates the number of carbon atoms per molecule of alcohol with the ratio of moles of carbonyl compound, ester, and unsaturated compounds present in alcohols derived from the process using isopropanol addition to the moles of these same undesired compounds in alkohols derived from the process using no isopropanol.

TABLE II.AVERAGE RESULTS FOR 10 WEIGHT PERCENT ISOPROPANOL ADDITION Carbon Moles carbonyl Moles ester Moles unsaturate No. of (ICaOH)/Mo1es (ICaOH)/Mo1es (IC3OH)/Mo1es unalcohol carbonyl (control) ester (control) saturate (control) In the fraction containing alcohols of more than 20 carbon atoms per molecule and other residual compounds, the fraction of the total alcohol was increased from 76 percent to 84 percent. The fraction of normal alcohols present was increased from 57 percent to 77 percent, by weight.

When the method of our invention is applied to a continuous process for manufacturing aluminum trialkoxide, the trialkylaluminum compound, for example, growth product in a suitable carrier liquid, is continuously contacted with a stream of oxygen or oxygen-containing gas to oxidize the trialkylaluminum compound to the desired point of partial oxidation. This can be accomplished in several ways, one consisting of flowing the trialkylaluminum through a contact tower in a flow path opposite that of a stream of oxygen-containing gas thereby partially oxidizing the trialkylaluminum. A desired amount of isopropanol is then continuously mixed with the efiluent partially oxidized trial-kylaluminum and the oxidation completed in a second contact column. Optionally the isopropanol can be added in the first column at a point in the lower part of the column and oxidation completed in the first contact column. The oxidized growth product can then be passed to a vacuum stripping column wherein the acetone and excess isopropanol are removed overhead; the aluminum trialkoxide removed from the bottom is passed to a second stripping column where the carrier liquid is removed. The oxidized trial'kylaluminum can then be further treated and hydrolyzed to alcohol.

Reasonable variation and modification are possible within the scope of the foregoing disclosure and the appended claims to the invention, the essence of which comprises, in the oxidation of trialkylaluminum compounds to the corresponding aluminum trialkoxides, the addition to the reaction of a quantity of isopropanol equal to between about 0.5 and 20 .weight percent of the trialkylaluminum compound reacted, when said oxidation is between about 70 and 100 percent complete.

We claim:

1. A process for converting aluminum alkyl compounds containing 2 to 30 carbon atoms in each alkyl group to aluminum alkoxide compounds, comprising:

(a) partially oxidizing the aluminum alkyl compounds with oxygen;

(b) adding isopropanol to the resulting partially oxidized aluminum alkyl compounds;

(c) completing the oxidation reaction; and

(d) removing acetone and excess isopropanol from the oxidation reaction product obtained.

2. The process of claim 1 wherein the isopropanol is added in an amount of between about 0.5 and about 20 weight percent of the aluminum alkyl compounds initially present at the beginning of the oxidizing step of (a).

3. The process of claim 1 wherein the isopropanol is added in an amount of between about 5 and about 10 weight percent of aluminum alkyl compound initially present at the beginning of the oxidizing step of (a).

4. The process of claim 1 wherein the isopropanol is added When the oxidizing step of (a) is between about 70 and 100 percent complete.

5. The process of claim 1 wherein the isopropanol is added when the oxidizing step of (a) is between about and about percent complete.

6. The process of claim .1 wherein said step (d) of removing acetone is accomplished by heating the oxidation reaction product to a temperature suflicient to volatilize acetone present in said product.

7. The process of claim 1 wherein said aluminum alkyl compounds contain 2 to 22 carbon atoms in each alkyl group.

References Cited UNITED STATES PATENTS 3,017,438 1/ 1962 Atwood. 3,104,251 9/1963 Foster et al. 3,257,468 6/1966 Dickey et al.

TOBIAS E. LEVOW, Primary Examiner. H. M. S. SN EED, Assistant Examiner.

US. Cl. X.R. 260-632 

